Extratropical response to the MJO

The Madden Julian Oscillation (MJO) has a systematic influence on the state of the extratropical atmosphere. The physical mechanism involves teleconnections from tropical deep convective heat sources through wave propagation. MJO heating resembles a propagating dipole that cycles through phases on a timescale similar to the response timescale. This complicates the attribution of the response to a well identified phase in the tropical heat source.

We have used DREAM to examine the extratropical response to a moving cyclic MJO-like tropical heat source based on OLR data. A set of ensemble forecast experiments and consistent stationary wave solutions have been analysed, together with longer equilibrium integrations, to investigate how the extratropical response relates to the phase of the MJO heating.

We find that the response is modified by the propagation of the source in a way that depends on the initial phase. The response also displays both stationary and transient nonlinearity which can account for an asymmetric response for opposite-phase dipole heat sources.

For further details see Hall et al, 2020 (submitted to Climate Dynamics).

Remote response to MJO

Propagating Source

Day-12 z500 from ensemble integrations of DREAM with simulated tropical deep convection fixed or propagating dipole